1. Field of the Invention
This invention relates to an automatic transmission, and more particularly, an automatic transmission with a small number of clutches, which enables multiple speeds.
2. Description of the Related Art
A plurality of planetary gearsets, clutches, and brakes are often used as an automatic transmission for a vehicle. The automatic transmission disclosed in Japanese Patent Laid-Open Publication No. 2000-199549 is one example of an automatic transmission in which three pairs of the planetary gearsets, three clutches, and two brakes enable six forward speeds.
However, because a clutch rotates, a drum, a seal ring, and a centrifugal hydraulic pressure balance mechanism in a cylinder chamber and the like are required. In addition, the weight and cost of clutches is more than those of brakes. The clutch is also disadvantageous in terms of a shaft length of the transmission.